Networks are known which support variable bit-rate transmission by partitioning user data into a sequence of so-called "cells" and inputting them asynchronously to the network. One such network is the Broadband Integrated Services Digital Network (B-ISDN) and is referred to as an Asynchronous Transfer Mode (ATM) network.
ATM networks allow video information to be transmitted with variable bit-rate (VBR). This, in turn, allows statistical multiplexing of data from a relatively large number of users for transmission over a single data channel. The transmission of the data is in ATM cells.
In the ISO Moving Picture Experts Group (MPEG1) audio-video coding standard (ISO 11172 Committee Draft of ISO-IEC/JCT1/SC29/WG11), a system multiplexing capability is provided in which an encoder periodically sends samples of its time clock called Clock References (Enc.sub.-- CRs). Typically, the Enc.sub.-- CRs are transmitted at the rate of a few a second.
One arrangement for recovery of timing in an ATM decoder is disclosed in our U.S. Pat. No. 5,287,182 issued Feb. 15, 1994. In the disclosed arrangement, recovery of the time clock at the decoder relies on averaging jitter effects over many received Enc.sub.-- CR values. In cases of extreme jitter, thousands of Enc.sub.-- CR values may be required before the decoder timing recovery circuitry converges to a stable operating condition. Because the Enc.sub.-- CR values are sent so infrequently, convergence of the decoder timing recovery circuitry can take a long time, for example, as long as 25 seconds. This would be unacceptable in most practical systems.